Synthesis and Reactivity of Unusual Palladium (II) Complexes Supported by a Diarylamido/BIS(Phosphine) PNP Pincer Ligand

This dissertation discusses the synthesis and reactivity of divalent palladium complexes supported by diarylamido bis-phosphine pincer ligands (PNP). The PNP is a tridentate pincer type ligand which typically adopts meridional type coordination. The rigidity and tight coordination of the PNP ligand provides the unique opportunity to study the coordination of ligands such as O_(2) and C_(2)H_(4) to a single coordination site on palladium, or the reactivity of a single empty coordination site trans to a weak trans-influencing ligand such as diarylamido. Irradiation of [(^(F)PNP^(iPr))Pd-]_(2) under an atmosphere of dioxygen irreversibly produces a mixture of a monohapto palladium(II) superoxide ((^(F)PNP^(iPr))PdO_(2)) and a palladium µ-peroxide ([(^(F)PNP^(iPr))PdO-]_(2)). Under photolytic conditions these two complexes are in equilibrium with each other. (^(F)PNP^(iPr))PdO_(2), an open-shell paramagnetic species, was characterized by a combination of single-crystal X-ray crystallography, EPR, and ^(19)F NMR spectroscopies. In addition, irradiation of [(PNP)Pd-]_(2) under an atmosphere of C_(2)H_(4) produces a mixture of [(PNP)Pd-]_(2) and a ethylene-bridged dinuclear palladium complex ([(PNP)Pd-CH_(2)-]_(2)). If the ethylene headspace is removed, and [(PNP)Pd-CH_(2)-]_(2) is irradiated it is completely converted to [(PNP)Pd-]_(2). This suggests that in the presence of ethylene these two complexes are in photolytic equilibrium with each other. In addition, this dissertation will also discuss the synthesis and reactivity of [(PNPR)Pd]^(+) (R = ^(i)Pr, ^(t)Bu) cations. [(^(F)PNP^(iPr))Pd]^(+) cations are highly electrophilic complexes that are able to coordinate Lewis bases such as THF, H_(2)O, and even extremely poor Lewis bases such as toluene and benzene. In addition, irradiation of [(^(F)PNP^(iPr))Pd]^(+) cations in bromobenzene induces the abstraction of a bromine atom from bromobenzene, consistent with a metalloradical species. Addition of dioxygen to [(^(F)PNP^(iPr))Pd]^(+) cations generates a paramagnetic, cationic η^(1) superoxide. In non-halogenated arene solvents [(^(F)PNP^(iPr))Pd]^(+) cations undergo a highly unusual photo-induced isomerization of the isopropyl groups on the supporting phosphines to n-propyl. This unprecedented isomerization is believed to occur via C-P bond cleavage and is driven by the decrease in sterics around the metal, which allows for the facilitated coordination of the arene solvent

L'Expansion de la Culture du Soja en Campèche, le Mexique: Problématique et Perspectives

The soybean is the grain in which greater food dependency has Mexico, reason why as of 2008, the government has promoted his culture, granting excellent subsidies, as much to producers as to buyers of the grain, thus contributing to a recent process of expansion in certain states, as it happens in Campeche. The objetive of this article is the analysis of the characteristics and effects of those supports, as well as of the rest of factors that until today they have taken to the producers of the mentioned state to initiate or to expand the cultivation of the soybean. The findings of the investigation reveal that although the producers have improved their levels of income, the process is vulnerable, as it depends on variables like the governmental supports, the international prices of the soybean and exchange rate. Although the study of the negative effects of genetically modified soybeans (GM) in other areas (environment, biodiversity, deforestation, human and animal health) is not the purpose of this investigation, some information will be provided, as on the conflict between soybean producers and beekeepers in the state of Campeche.La soja es el grano en el que mayor dependencia alimentaria tiene México, por lo que a partir de 2008 el gobierno ha promovido su cultivo, otorgando relevantes subsidios, tanto a productores como a compradores del grano, contribuyendo así a un reciente proceso de expansión en ciertos estados, como ocurre en Campeche. Este artículo tiene como objetivo el análisis de las características y efectos de dichos apoyos, así como del resto de factores que hasta hoy han llevado a los productores del mencionado estado a iniciar o expandir el cultivo de la soja. Los hallazgos de la investigación revelan que si bien los productores han mejorado sus niveles de ingreso, el proceso es vulnerable, al depender de variables como los apoyos gubernamentales, los precios internacionales de la soja y el tipo de cambio. Aunque el estudio de los efectos negativos de la soja genéticamente manipulada (GM) en otros ámbitos (medio ambiente, biodiversidad, deforestación, salud humana y animal) no es el objetivo de la presente investigación, se proporciona información al respecto, al igual que sobre el conflicto existente entre los productores de dicha soja y los apicultores del estado de Campeche.Le soja est le grain dans lequel une plus grande dépendance alimentaire a le Mexique, ce pourquoi à partir de 2008, le gouvernement a promu sa culture, en accordant des subventions significatives, tant à des producteurs comme à des acheteurs du grain, contribuant ainsi à un récent processus d'expansion dans certains états, comme il se produit en Bois de Campèche. Cet article a pour but l'analyse les caractéristiques et les effets de ces appuis, ainsi que du reste de facteurs que jusqu'à aujourd'hui aux producteurs de l'état mentionné à entamer ou ils ont développé la culture du soja. Les découvertes de la recherche révèlent que bien que les producteurs ils ont amélioré leurs niveaux de recette, le processus est vulnérable, en dépendant de variables comme les appuis gouvernementaux, les prix internationaux du soja et le taux de change. Bien que l'étude des effets négatifs de soja génétiquement modifiées (GM) dans d'autres domaines (environnement, la biodiversité, la déforestation, la santé humaine et animale) ne sont pas le but de cette recherche, certaines informations seront fournies, comme sur le conflit entre les producteurs et les apiculteurs de soja que l'état de Campeche

Synthesis and Reactivity of Unusual Palladium (II) Complexes Supported by a Diarylamido/BIS(Phosphine) PNP Pincer Ligand

This dissertation discusses the synthesis and reactivity of divalent palladium complexes supported by diarylamido bis-phosphine pincer ligands (PNP). The PNP is a tridentate pincer type ligand which typically adopts meridional type coordination. The rigidity and tight coordination of the PNP ligand provides the unique opportunity to study the coordination of ligands such as O_(2) and C_(2)H_(4) to a single coordination site on palladium, or the reactivity of a single empty coordination site trans to a weak trans-influencing ligand such as diarylamido. Irradiation of [(^(F)PNP^(iPr))Pd-]_(2) under an atmosphere of dioxygen irreversibly produces a mixture of a monohapto palladium(II) superoxide ((^(F)PNP^(iPr))PdO_(2)) and a palladium µ-peroxide ([(^(F)PNP^(iPr))PdO-]_(2)). Under photolytic conditions these two complexes are in equilibrium with each other. (^(F)PNP^(iPr))PdO_(2), an open-shell paramagnetic species, was characterized by a combination of single-crystal X-ray crystallography, EPR, and ^(19)F NMR spectroscopies. In addition, irradiation of [(PNP)Pd-]_(2) under an atmosphere of C_(2)H_(4) produces a mixture of [(PNP)Pd-]_(2) and a ethylene-bridged dinuclear palladium complex ([(PNP)Pd-CH_(2)-]_(2)). If the ethylene headspace is removed, and [(PNP)Pd-CH_(2)-]_(2) is irradiated it is completely converted to [(PNP)Pd-]_(2). This suggests that in the presence of ethylene these two complexes are in photolytic equilibrium with each other. In addition, this dissertation will also discuss the synthesis and reactivity of [(PNPR)Pd]^(+) (R = ^(i)Pr, ^(t)Bu) cations. [(^(F)PNP^(iPr))Pd]^(+) cations are highly electrophilic complexes that are able to coordinate Lewis bases such as THF, H_(2)O, and even extremely poor Lewis bases such as toluene and benzene. In addition, irradiation of [(^(F)PNP^(iPr))Pd]^(+) cations in bromobenzene induces the abstraction of a bromine atom from bromobenzene, consistent with a metalloradical species. Addition of dioxygen to [(^(F)PNP^(iPr))Pd]^(+) cations generates a paramagnetic, cationic η^(1) superoxide. In non-halogenated arene solvents [(^(F)PNP^(iPr))Pd]^(+) cations undergo a highly unusual photo-induced isomerization of the isopropyl groups on the supporting phosphines to n-propyl. This unprecedented isomerization is believed to occur via C-P bond cleavage and is driven by the decrease in sterics around the metal, which allows for the facilitated coordination of the arene solvent

Emociones y ciudad: los motines de pachucos y la prensa del noreste estadounidense

El objetivo del presente artículo es revisar el papel de la prensa estadounidense como generadora y difusora de emociones hacia ciertos sujetos urbanos. Parto del presupuesto de que las emociones tienen un papel importante en la configuración de las identidades nacionales, locales y grupales (etarias, genéricas, raciales). Las normativas sobre sus formas y momentos (apropiados) de expresión o contención contribuyen a legitimar, subordinar y diferenciar distintos grupos que conviven en un mismo espacio. En el caso de esta investigación, mi análisis se centra en el estudio del manejo de las emociones por parte de la prensa del noreste estadounidense durante los llamados zoot-suit riots o motines de pachucos protagonizados por jóvenes marinos y adolescentes mexicoamericanos en la ciudad de Los Ángeles, California, en el verano de 1943. Mi interés es encontrar similitudes y diferencias en la forma de abordar e interpretar la emocionalidad entre la prensa de dos espacios geográficos distantes: el suroeste y el noreste de Estados Unidos, y determinar si la particularidad de sus desarrollos históricos interviene en la interpretación y lectura emocional, racial y etaria de los acontecimiento

Subsidios gubernamentales para riesgos de mercado en granos: el caso del sorgo en México

In a context of extreme price volatility related with agricultural commodities, as the one present during the last years, the producer protection is very relevant. For this purpose, the Mexican government established a program called contract farming, which characteristics and limitations is the object of this study. We found that the program offers important benefits to the participants, although is very vulnerable given the contract breach related to climatic disasters, the relation between prices (international vs. domestic) and the evolution of the exchangerate. Other obstacles of the program are the reduced national coverage and the concentration of subsidies in a reduced group of beneficiaries,among them relevant agribusiness.En un contexto de gran volatilidad de los precios internacionalesde los granos, como el vivido en los últimos años, la protección alos productores adquiere gran relevancia. Con este fin, el gobierno deMéxico implementó un programa de subsidios llamado agricultura porcontrato, cuyas características y limitantes son el objeto central de nuestroestudio. Entre los hallazgos, se encontró que si bien dicho programaofrece importantes ventajas para los participantes, es sumamante vulnerablepor los inclumplimientos de contratos motivados por los efectosadversos del clima, la relación de precios relativos (precios internacionalesvs precios en el mercado libre) y la evolución del tipo de cambio.Otras limitantes son la reducida cobertura nacional y la concentración delos apoyos en un reducido grupo de beneficiarios, entre los que figurangrandes empresas alimentarias

Globalización, agroindustrias y agricultura por contrato en México

Contract farming comprises an agribusiness supply mechanism thas undergone rapid expansion in recent years. Among the factors influencing that expansion are changes in consumption, the growth and strengthening of agribusinesses and other distributors, and the application of structural adjustment policies. The objective of this article is the analysis of the characteristics of the type of contract farming practiced with regard to the production of pickling cucumbers, as well as its effects on producers, labor and land markets, and the environment. We find that the income obtained by contracted producers has not freed them from the necessity of diversifying their activities, and that, in general, their situation as producers of non-traditional commodities is vulnerable and dependent upon global markets.La agricultura por contrato constituye un mecanismo de abasto de las agroindustrias que se ha expandido aceleradamente en las últimas décadas. En ello han influido los cambios en el consumo, la expansión y fortalecimiento de las agroindustrias y otros distribuidores, y la aplicación de políticas de ajuste estructural. El objetivo de este artículo es el análisis de las características de la agricultura por contrato practicada en torno a la producción de pepinillos de exportación, así como de sus efectos en los productores, mercados de trabajo y de tierras y medio ambiente. Encontramos que los ingresos obtenidos por los productores contratados no los han librado de la necesidad de diversificar sus actividades, y que en general su situación como productores de bienes no-tradicionales es vulnerable y dependiente de los cambiantes escenarios de los mercados globales